1. Aerosol Radiative Forcing from combined MODIS and CERES measurements
Sundar A. Christopher
University of Alabama - Huntsville
Jianglong Zhang
Lorraine A. Remer
Yoram Kaufman
Introduction
MODIS/CERES
Aerosol effect
Aerosol forcing
Outstanding issues
Research Objective : To use merged MODIS/CERES
Data to examine aerosol effects on radiation
Christopher and Zhang, GRL – September, 2004
Zhang, Christopher, Remer, Kaufman, JGR- Part
Zhang, Christopher, Remer, Kaufman, JGR- Part
Christopher, Zhang, Remer, Kaufman, GRL – submitted – 2005
Yu et al – ACPD – 2005 – CCSP
Anderson et al – BAMS
MODIS Science Team meeting,
January 2006

2. Aerosol Direct Effects
Aerosol effects are being examined increasingly from measurement based approaches since Terra/Aqua (Yu et al. ACPD-CCSP, 2005, Anderson et al. BAMS, 2005)
Direct radiative effects include change in net radiative flux at TOA from all aerosols.
Aerosol Climate forcing is for anthropogenic aerosols.

3. Aerosol Effects – Satellite AOT + RT model
Satellite derived AOT (e.g. MODIS) plus RT model. – e.g. Boucher et al
Satellite derived AOT with MODIS aerosol properties – Remer and Kaufman, 2005.
Mostly over oceans unless high AOT - regional
Chou et al - SeaWIFS,
Boucher et al – POLDER,
Christopher et al – GOES – Regional/land
Remer and Kaufman - MODIS
MODIS AOT
Satellite + CTM
Yu et al (ACPD)
Chung et al (JGR-2005)

4. MODIS/CERES Fusion CERES Footprint CERES - 20X20 km2 nadir
Imager
Pixel
CERES
Footprint
CERES - 20X20 km2 nadir
MODIS AOT – 10X10 km2
Point spread function
Weighted MODIS aerosol
Within CERES footprint –
CERES SSF ~ 1 year of data
Cloud Fraction
AOT at 550 nm
Fine Mode fraction
CERES radiance and flux
Cloud free only
DRE = Fclear – F aerosol
CERES Broadband SW radiance
Cross track scanner
RAP mode : For Angular Models
Ongoing work : Data fusion of MODIS/MISR/CERES for aerosol research
Terra swath
CERES
MODIS
MISR

5. CERES SSF (Merged MODIS and CERES)
Recent progress
Sample bias accounted for
Using MODIS narrowband to
CERES broadband conversion
(Loeb and M-Smith 2005)
2. Bulk sample bias adjustments
Using forcing efficiencies
(Christopher & Zhang 2004)
3. Aerosol angular model using
CERES RAP data (Zhang et al.) as
function of AOT, aerosol fine
mode fraction, wind speed.
CERES SSF
Point spread function weighted aerosol and cloud properties from MODIS L2 within CERES footprint
Most studies focus on cloud-free pixels over near-global oceans

6. Angular Models ERBE : Over cloud free oceans
No aerosol aerosol properties
No wind speed
TRMM : Over cloud free oceans
Include ECMWF wind speed
Use theoretical calculation to account
for the effect of aerosol optical depth on TOA radiation fields
New Terra ADM : Over cloud free oceans
Use SSM/I wind speed
Use the fraction of small mode to total
AOT ()
More coverage compared to TRMM
MODIS : more accurate for aerosol research
Significant differences

7. MODIS AOT and CERES derived SWARF for NDJF
Uncertainties
Measurements
Cloud contamination
Retrievals (AOT,)
Methods
(ADM,
Clear sky characterization)
CERES Forcing wm-2
MODIS AOT
Instantaneous Forcing Efficiency ~ -60 Wm-2/AOT

8. Aerosol Radiative Effect from Terra
~ 1 year spatial
distribution
Cloud-free
CERES Forcing
-5.31.7 Wm-2
NH forcing 1.5 times greater than SH
Global mean value over oceans compare
Well among methods although regional
differences exist.
Christopher and Zhang, GRL, 2004
Zhang et al, JGR, 2005, Part 1 and Part 2

9. Fine Mode (Anthropogenic) Shortwave Aerosol Forcing
Dust
Anthropogenic
Marine f
Cloud free anthropogenic forcing : Wm-2
From MODIS/CERES – Compares well (same mean value!) with recent Kaufman et al (GRL, 2005) work. – Christopher et al (submitted, GRL, 2005).
550 =  anthropogenic +  dust + marine
550f550=faa+fmm +fdd
fa =0.920.03, fd =0.510.03 fm =0.320.07
a =[(f550-fdust)550 -(fm-fdust)m]/(fa-fd)
Christopher and Zhang, 2002;2004, GRL

10. Summary
Merged MODIS/CERES product is an excellent data set for studying aerosol radiative effects although proper Angular models required.
New angular models developed not only as a function of AOT and wind speed but fine mode fraction that facilitated study of anthropogenic aerosol forcing.
Global TOA aerosol direct effect of -5.3±1.7 Wm-2 is in good agreement with previous studies.
Anthropogenic (fine mode) aerosol forcing from CERES/MODIS data is -1.4 ±0.8 Wm-2 which is in agreement with recent estimates by Kaufman et al (2005)..

11. Future Directions Cloud Free to all sky conditions
Multi-year MODIS/CERES anthropogenic aerosol forcing
Aerosol over land MODIS/CERES
MODIS/MISR/CERES data fusion for aerosols over bright targets
CERES and CTM Fusion

12. Multi sensor approach for aerosol research
MODIS (MOD06) for cloud clearing
MISR for AOT – Bright Targets
CERES for LW fluxes
Longwave forcing : +7 Wm-2.